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Sunday, March 29, 2009

DIY aquarium chiller

My nano reef aquarium is usually 2-3*F hotter than the ambient room temperature (after the heater setpoint has been reached). This is a problem, since the temperature in my living room is often higher than 82*F in the summer. This puts the tank water at an uncomfortably high temperature (84+), and I think that the corals suffer from the temperature swings as well as the overall high values.

So, how to lower the tank temperature? For a 5 gallon tank like mine, a peltier heat pump like the Coolworks Ice Probe would seemingly be a good choice. I tried building just such a device a few years ago, and it was a big failure. I learned that peltier heat pumps cannot be controlled by raw pulse width modulation (PWM) signals, and they don't do well in thermostatic (on/off) systems either. One reason is that the semiconductors inside the Peltier device do not like the thermal shock of the constant on/off switching. Also, Peltier heat pumps are already horribly inefficient, and using PWM or on/off control makes things even worse. During the "off" cycle of either the PWM pulse or the on/off cycle, the heat will flow backward though the device -- the same heat that the device just pumped during the "on" part of the cycle. Think of bailing out a sinking boat with a bucket that has a huge hole in the bottom. The best way to control the peltier modules is to generate high-frequency PWM, then smooth it out with an inductor/capacitor filter. There is still the problem of the peltier junction's inefficiency, and the hot-side heatsink must be massive with a massive fan to make the system viable. Anyway, I haven't heard anything great about the Ice Probe, nor any other Peltier cooling systems designed for any application that requires a good amount of cooling. I have a thermoelectric refrigerator that is just marginally good enough for its purpose.

So, today's design for a new aquarium chiller will NOT use Peltier junctions, as much as I love the idea. I bought a $99 water cooler that uses a conventional compressor and r-134a refrigerant.I filled the cooler with tap water, and mounted a Rio pump with an outgoing hose and return line.

The two hoses connect to a stainless steel coil. I've had this thing laying around my shop for a long time. It came out of junked, expensive lab equipment. It is non-magnetic, which indicates 3-series stainless steel. I'm guessing it's 316, which is highly corrosion resistant. Of course, the aquarium purists would insist on titanium, but I don't have any, nor do I think it's really necessary. I'd love to hear from anyone who saw a stainless steel chiller coil corrode, or definitively caused tank poisoning.

I melted a couple slots in my hang-on cheapo protein skimmer (it's not a Skilter, but very similar). I would have used a dremel, but I didn't feel like taking the filter off the tank, and I also wanted to avoid getting plastic shavings in the water. The stainless coil sits down into the slots and is just held by gravity.

The cooler is plugged in all the time. It keeps its insulated water chamber around 47*F. The Rio pump in the cooler is turned on and off by the PID temperature controller that I mentioned in a previous blog post. The controller can be configured to use a longer cycle time (eg 30 seconds) since it is controlling a pump, and it would not make sense to turn a pump on and off once per second as it would be for a heater.

The cooler is rated 86 watts. If this is what the compressor draws while normally running (I didn't check it). I would estimate the cooler can pump about 170 watts of heat (about 580 btu/hr). The coefficient of performance is around 2 for small compressor systems. For comparison, a large peltier device can move around 70W under ideal conditions, at a very specific current/voltage. The coefficient of performance for Peltier devices usually tops out around 1, and is often about 0.5 for realistic situations. So, a peltier pump drawing 86 watts, would only pump about 43 to 86 watts of heat.

I just installed this chiller today, so I'll monitor it on hot days and make another post about its performance.

Thanks for the comment. So far, it hasn't been too hot here (Sunnyvale, CA). Since I setup the chiller, the hottest temperature in my living room was about 78*F. At that ambient temperature, the PID temperature controller was using about 2 to 5% of the chiller's capacity. The tank setpoint is 80*F, so the normal 2-3*F rise over ambient temperature was easily controlled by the chiller. It will be interesting to see how it works when the room is 85*F or more, as it often gets on summer days. I think using a water cooler for a chiller is a much better approach than using a small dorm refrigerator because you never have to rely on air as a transfer medium. I'll post more when it gets hot here.

Great! I hope my blog has been helpful. I looked at your Peltier cooler, and it seems like you are almost done. I think you were smart to use the refrigerator's original power supply and controller. Since the refrigerator's temperature range is well below the aquarium's, I would imagine your Peltier runs %100 when it is on. This is good for best efficiency. Good luck!

im new to this but im curious how you hook it up to the system inside using a pump what cause the water to go back in teh nak and not like over flow ? also when you buy a chiller do you have to buy a pump with them as well ? not much info i can find what i need to set one up

Anonymous, you will need a water cooler, a small water pump, a couple lengths of plastic tubing, and a heat exchanger coil (simply a coil of metal pipe -- stainless or titanium). The aquarium water does not leave the aquarium, so there is no danger of flooding. Instead, the water cooler is filled with tap water, and the small water pump moves the tap water from the cooler through the heat exchanger coil and back into the cooler. Thus, the aquarium water is entirely separate from the water in the cooler.

Most commercial chiller units also require a pump, but these typically move the aquarium water itself. Some chillers have an immersion coil that can be placed in your sump, and thus do not need a separate pump.

As I mentioned in the article, the heat exchanger coil that I used came out of junked lab equipment. You'll need a length (or pre-made coil) of stainless steel tubing. Try this:http://www.mcmaster.com/#89995k411You'll need to bend it into a coil, but be careful; the tubing may collapse if you try to bend it too tightly.

Hey Ben :)I'm researching DIY Watercooler/aquarium chillersand I wound up here :) It's been nearly a year....how well do you like your results?I never knew there even were such things as 'aquarium chillers' til recently...boy, they're expensive :O Like you, my application is small, I really can't justify the expense. I've got a 20Lthat needs to be in the low 60s F. (Add to that, very low-end flow...too much current is stressful)The house is set at 78....come summertime, it'll likely be in the 80s even with the A/C on.I've been getting by with fans, but summer's coming, so I'm thinking DIY chiller. Do you suppose the setup that you have would meet my needs?Thanks in advance :)Rick

Rick, the chiller worked very well over the course of last summer. My living room is usually in the 80's *F, and the aquarium temperature never rose about the setpoint. My stainless cooling coil did not last, though. It started to rust, and I plan to replace it with a titanium coil for the coming summer. Search my blog about passivating stainless steel -- my attempts did not work.

For your application, you need a 20*F difference minimum between tank temperature and room temperature. This will require a lot of cooling power -- much more than the 10*F max differential in my setup. If you have halide lighting, you'll need even more cooling power. If you find a used water cooler on craigslist, it will probably be very cheap, and worth a try. Even buying a new one for $100 might be worth it. Don't bother with anything that uses Peltier junctions. You need a refrigerant system to move lots of heat. Good luck -Ben

Hey Ben. so far from all the research i have been doin your DIY seems to be the most feasible. i live in southern India on the west coast of the country and my ambient temp during summer reaches 34 with my water temp reachin 32 (i keep my room well ventilated) and during the monsoons the temps are between 24 to 28.

am plannin to set up a few tanks for some overly sensitive to temp shrimps like the saluwasi which needs the temp to remain at a maximum of 24c. will your idea work and can i use them in multiple tanks?

Zakk, if your tank is small enough and the water cooler is powerful enough, your water temp will stay in the correct range. Water cooler are so much less expensive than aquarium chillers, it will pay to experiment.

Anonymous, you could possibly reconfigure a water cooler so that it fits into an aquarium stand. You may need to cut the refrigerant lines, and place the condenser coil on the back of your stand horizontally. You would then need to evacuate the refrigerant lines and refill. Luckily, many small water coolers use r134a, which is easily bought in auto parts stores. I've done exactly this procedure with other small refrigeration projects.

I'm betting the compressor could run continuously for years without any trouble.

hi I am from southern india. Here the temp is, maximum 35–40 °C (95–104 °F) and minimum 15–22 °C (59–72 °F). Also we have frequent power problems. I have tried dolphin peltier chiller and it did not work. I have been looking for a decent explanation of using a water chiller. I can get a second hand one here. The questions i want to ask are,1. What should be the compressor capacity?2. Can it cool in this weather?3. Can it run on an invertor?

Ajeet, modern inverters should be able to run a compressor without any problem. I don't know the answers to your other questions since answering them would require a fair bit of research into the cooling capacity of the chiller, heat load on your tank, airflow, etc. Good luck.

could be an effective tig torch water cooler, though many simply run ambient water through the torch without any cooling at all. something to consider putting into the loop. put the heat exchanger coil in the cooler pond or just draw chilled water out of the tank directly. I am setting up a Diy torch cooler now so thanks for the idea.

Ben - came across your blog while searching for aquarium chillers. Not sure if it is still active. I saw your comments about Peltier based chillers and as a manufacturer of Peltier subassemblies thought I would comment. Peltier modules can be very efficient achieving COP > 1 (like any heat pump) under the right operating conditions, i.e., moderate temperature differentials and operating current levels less than the Imax rating (see the COP curves on any site selling Peltier modules). Peltier modules (aka TECs) are modular in nature, so if more cooling is required scaling the chiller size (heat sinks and TECs) will usually satisfy most application requirements. Heat sinks do not need to be massive, just efficient and this includes the fan performance and the air flow profile through the heat sink fins or pins.

The performance and quality of the TECs from different manufacturers vary considerably will affect the net chiller performance as well, some of the TECs produced in China are very good, some are pretty poor. Marlow Inc., a US company manufactures very good and high performing TECs. Generally you pay for what you get. PWM is a very good way to power Peltier based assemblies especially when coupled with a PID controller chip to avoid cycling and harsh applications of power. Most TEC manufacturers recommend a min. frequency of 800 Hz, but some studies show that a PWM frequency as low as 200 Hz is not detrimental. These are not a high PWM frequencies and thermally the TEC doesn't see these cycles. On/off controllers with relays should be avoided. With proper temperature control, Peltier based assemblies should operate > 100,000 hours, although the fans will not last this long. Failure of TEC due to thermal fatigue should be easily avoided with proper design.

If the heat load can be accurately estimated, the max. ambient temperature and max. or min. water temperature specified there is no reason why a Peltier based chiller cannot be designed and work well for aquarium applications, especially with a titanium tubed liquid plate. It would be a lot more compact, quieter and can also be controlled to seamlessly cool or heat depending on the ambient temperature swings. Bi-directional temperature control is more difficult with Freon based systems. Larry Filler, Principal, Allied Thermal Designs, Windham, NH